Heparin is an effective and safe blood anticoagulant. However, because of its hydrophilicity and large molecular size, the therapeutic use of heparin is limited by the need to administer it parenterally. A great deal of effort has been spent on the development of adjuvants, derivatives, analogue and expedients, to render heparin absorbable from the intestine, so that it may be orally administered. So far these efforts have not been successful. We have developed a mode of heparin ammonium ion complex which, when it was administered orally, gave sustaining systemic anticoagulant effect in rats. The optimal results should be able to attain by varying the molecular size of heparin molecule, lipophilicity of ammonium ion, etc. Methods as to the preparation of these ammoinium salt, the size characterization of heparin fractions and the pharmarcokinetics and toxicology experiments in rats and mice are outlined in this research project.